List of Abstracts

Clusters of galaxies confront us with two facts that gravity alone cannot explain. Their hot atmospheres hold most of the metals their galaxies ever made, and they carry more entropy than gravitational collapse can supply. Both point to the same source: energy and enriched gas injected by active nuclei as the cluster assembled. I will argue that in powerful radio galaxies at high redshift we are watching that injection happen, and that we can now follow it from the scale of the accretion disk out to the scale of the protocluster.

The evidence on small scales is the genesis of a wind. JWST/MIRI spectroscopy of the Spiderweb galaxy at z = 2.16 resolves a forest of coronal lines spanning a wide range of ionization, and every one of them carries a blueshifted wing. This is a multiphase wind caught at its launching point, chemically enriched in the α elements, and easily powered by the radio source: the mechanical output of the jet exceeds what the wind carries by orders of magnitude, so what limits the flow is not energy but how well it couples to, and loads mass from, the gas around it. Integrated over the lifetime of a radio episode, such a source delivers 10⁶⁰–10⁶¹ erg — the right order to supply the excess entropy of a present-day cluster atmosphere, and delivered together with the metals that atmosphere is observed to carry. The wind's mass and momentum fluxes grow with radius, so it plausibly never escapes the halo at all; far from being a shortcoming, that is what the argument requires, since the heat and the metals must stay where the intracluster baryons will settle.

On larger scales we see the consequences. ALMA and ATCA reveal of order 10¹¹ M⊙ of cold molecular gas spread through the halo in CO and [C I], gas that is already substantially enriched, and the first detection of water in an unlensed distant galaxy falls directly on the radio-jet structures — the signature of the jet working shocks into the circumgalactic medium, as does the warm molecular hydrogen JWST finds at the nucleus, excited by mechanical energy rather than by starlight. That same medium is forming stars in situ across roughly a hundred kiloparsecs, building an extended envelope of the kind that surrounds brightest cluster galaxies today.

The cycle is not one-way. In 4C 41.17 at z = 3.8, ALMA traces a cold stream of comparable mass falling inward along a cosmic filament. Accretion supplies the gas and the gravitational energy, the nucleus returns heat and metals, and the mixture cools, forms stars, and is driven out again. The intracluster medium is the residue of that cycle, and at high redshift we can watch it being made.

How strongly does dark matter interact with itself? Merging galaxy clusters should be the ideal place to find out, but the standard approach has stalled. Dark matter–galaxy offsets turn out to be intrinsically tiny — galaxies stay tightly coupled to the dominant halo potential — and whatever signal survives is entangled with the unknown merger phase, geometry, and initial conditions.

I will present a way around this. Double radio relics trace the pair of shocks launched at pericenter, and the shock-to-shock distance time-stamps precisely where a merger sits in its post-pericenter evolution. The trick is that shock propagation is nearly blind to the self-interaction cross-section, while the halo-to-halo separation is dragged inward by it — so the ratio of the two distances translates directly into σ/m.

Applied to a gold sample of eleven mergers hosting symmetric double relics, this yields σ/m < 0.22 (0.63) cm²/g at 68% (95%) confidence. It is the first cluster-collision constraint to marginalize fully over mass, viewing angle, collision speed, merger phase, impact parameter, and gas profile slope. I will close with what this rules out among SIDM models, and how the method sharpens as upcoming radio surveys expand the relic sample.

Galaxy cluster mergers provide unique laboratories for studying dark matter and cluster assembly. As the most massive gravitationally bound structures in the Universe, their merging can serve as cosmic dark matter colliders, enabling the study of energy scales that are impossible to reproduce on Earth. However, merging clusters are often highly disturbed and complex, and understanding their merger geometry requires observations across multiple tracers and spatial scales. In this talk, we present JWST strong- and weak-lensing analyses of two merging galaxy clusters, the Bullet Cluster and Abell 2744, complemented by multiwavelength observations. In the central region of the Bullet Cluster, the reconstructed dark matter distribution shows close agreement with the intracluster light, suggesting that the ICL can serve as a visual stellar tracer of detailed dark matter morphology even in a highly disturbed merger. In the core of Abell 2744, the geometry of mass bridges connecting the main clumps suggests merger axes that are closely aligned with the observed radio relics. Extending the analysis to larger fields, we examine how these merger signatures connect to the surrounding environment. Around Abell 2744, we find filamentary structures aligned with the inner mass elongation and merger axes. In the Bullet Cluster, wide-field radio observations reveal a radio relic candidate in the outskirts, located along the direction of the mass elongation inferred from the lensing analysis. These results highlight the need to study merging clusters across multiple scales and the synergy between JWST and upcoming wide-field surveys.

Distant Hot Dust-Obscured Galaxies (Hot DOGs) are extreme examples of luminous quasars that are heavily enshrouded in dust and exhibit fast-moving outflows on galactic scales. Recent James Webb Space Telescope observations reveal that high-redshift Hot DOGs exhibit some of the most extreme outflow velocities, with theoretical models indicating these winds are dust-driven by the radiation pressure from the quasar. Given these extreme outflows, it is important to understand the impact and potential feedback to the host galaxies and its circumgalactic medium (CGM). Here we present Keck Cosmic Webb Imager (KCWI+KCRM) observations of HotDOGs at z = 2.0-3.1, targeting their diffuse CGM through Ly⍺, CIV 1548, 1551, and HeII 1640 emission lines. Our survey aims to measure the extent of the Ly⍺, HeII 1640, and CIV emission and compare it to the CGM of similar bolometric luminosity quasars. We aim to explore the extent and distribution of ionized gas on CGM scales of the environments of Hot DOGs and search for evidence of companion galaxies to better understand the environment around these most obscured quasars, while measuring the contribution of gas to the CGM through potential merger activity and outflows.

The Big Bang has been typically identified as the beginning of the Universe: an event occurring at the “t = 0” moment of time, arrived at by extrapolating back our expanding Universe to a state of arbitrarily high temperatures and densities. Several lines of evidence converge on this picture, namely the major cornerstones of the Big Bang: the expanding Universe, the leftover bath of radiation observable as the cosmic microwave background, the abundance of the light elements forged during an early period of nucleosynthesis, and the growth and evolution of cosmic structure in our Universe. While the extrapolation back to a singularity, naively, is justifiable in an expanding Universe under the rules of General Relativity, those conditions would have led to observable effects that run contrary to what we see. Instead, the Universe is better described by cutting off the matter-and-radiation dominated Universe at some early time, patching on an inflationary epoch where space is expanding exponentially and dominated by some sort of vacuum energy. This is not mere theory more than 40 years on, but is supported by a vast suite of observable evidence. The case for this conclusion, even in the absence of B-mode polarization in the CMB, is laid out here, in the context of the full suite of cosmic evidence that supports, but is not limited by, the Big Bang picture alone.

Hyperluminous infrared galaxies (HyLIRGs) are the rarest and most extreme starbursts and found only in the distant Universe (z ≳ 1). They have intrinsic infrared (IR) luminosities LIR ≥ 10^{13} L⊙ and are commonly found to be major mergers. Recently, the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts project (PASSAGES) searched ~10^4 deg2 of the sky and found ~20 HyLIRGs. We describe a detailed study of PJ0116-24, the brightest (μLIR ≈ 2.6 × 10^{14} L⊙, magnified with μ ≈ 17) Einstein-ring HyLIRG in the southern sky, at z = 2.125, with observations from the near-IR integral-field spectrograph VLT/ERIS and the submillimetre interferometer ALMA. We detected Hα, Hβ, [N ii] and [S ii] lines and obtained an extreme Balmer decrement (Hα/Hβ ≈ 8.73 ± 1.14). We modelled the molecular-gas and ionized-gas kinematics with CO(3–2) and Hα data at ~100–300 pc and (sub)kiloparsec delensed scales, respectively, finding consistent regular rotation. We found PJ0116-24 to be highly rotationally supported (vrot/σ0, mol. gas ≈ 9.4) with a richer gaseous substructure than other known HyLIRGs. Our results imply that PJ0116-24 is an intrinsically massive (Mbaryon ≈ 10^{11.3} M⊙) and rare starbursty disk (star-formation rate, SFR = 1,490 M⊙ yr−1) probably undergoing secular evolution. This indicates that the maximal SFR (≳1,000 M⊙ yr−1) predicted by simulations could occur during a galaxy’s secular evolution, away from major mergers. 

Massive galaxy clusters act as gravitational telescopes, magnifying background supernovae that would otherwise remain undetectable and, in favourable geometries, producing multiple images of the same explosion [1]. The delays between those images give a measurement of the Hubble constant that is independent of both the local distance ladder and the cosmic microwave background, and therefore bears directly on the tension between them [2]. Magnification also opens access to the high-redshift supernova population, whose rates constrain the cosmic star formation history.

I will present our past and ongoing ground-based efforts to find and study these events. Targeted near-infrared campaigns towards galaxy clusters allowed us to measure volumetric core-collapse supernova rates, found to be in agreement with the star formation history, as well as supernova rates for the cluster galaxies themselves [3,4]. Magnification also makes possible spectroscopy that would otherwise be out of reach, which we have used to test whether the intrinsic properties of Type Ia supernovae evolve with redshift, a potential systematic for dark energy measurements [5,6].

I will then turn to the ongoing VST campaign monitoring galaxies and clusters that host gravitationally lensed quasars at roughly daily cadence. This provides both the temporal resolution needed for time delays and the wide field needed to find supernovae in cluster member galaxies, which give an independent distance to the lens [7]. Finally, I will show some of our ongoing efforts within the Euclid-LSST lensed transient search.

Lensed supernova discoveries are expected to increase significantly in the coming years. Well sampled time delays and the identification of cluster-member supernovae both require years of wide-field monitoring that space facilities cannot provide, so ground-based surveys remain essential alongside JWST.

The 10¹²⁰ orders of magnetude discrepancy between the observed cosmological constant and quantum field theory (QFT) predictions remains a central enigma in modern cosmology. This study provides a rigorous analytical derivation of the value 10¹²² by treating gravity as an entropic force arising from information-theoretic constraints. It demonstrated that this result can be derived through aligns precisely with BEKENSTEIN-HAWKING entropy, HAWKING temperature, and Penrose’s information concept. Furthermore the derived dynamic dark energy density A (t), was validated against empirical data from the Max Planck Institute for Radio Astronomy (Planck Mission). Showing exact agreement based on a cosmic age of 13.82 billion years. By linking the „naturalness problem“ to the evolution of cosmic entropy, this study suggests that the accelerated expansion of the universe is an emergent phenomenon bridging the gap between quantum information theory (QIT) and general relativity theory (GRT), driven by the evolution of cosmic entropy. Establishing a direct link between the bit density of the universe and the dynamic nature of dark energy, the study offers a potential resolution to the cosmological constant problem.

The presented article provides a theory of dark energy that appears to have been developed in two complementary ways. On the one hand, this theory is based on physics and mathematics and, on the other hand, it is veryficated on the basis of available data. This correspondends to the discovery of the laws of planetary motion in elliptical planetary orbits by JOHANNES KEPLER in the past. He developed his laws from a large amount of data. Later it was substantiated more thoroughly by ISAAK NEWTON.

The focus is on deriving a formula for the equivalence of energy and time or equivalence of dark energy and the age of the universe. For the first time, this made it possible to calculate the exact value of dark energy. The dark matter of the cosmos is calculated. This derivation of a formula for the equivalence of energy and time provides new theoretical insights and applications in theoretical terms and leads to the discovery of a new law of nature.

The theoretical result is confronted with the numerical value calculated from the available data from the MAX PLANCK Institute for Radio Astronomy. Excellent matching of numerical values of dark energy resulting in four independent paths (by physical-mathematical derivation, derivation on the basis of available data, by STEPHEN HAWKING's contribution, By ROGER PENROSE's contribution with the concept of information) makes the approach plausible.

It is shown that all the information of the universe is encoded on the PLANCK-scale and is „unrolled“ into spacetime by factor t_u (age of the universe) → Holographic Principle.

The fact that the theoretically derived value of the HUBBLE constant (H₀) lies well within the range of astronomical measurements is the strongest indication that the connection between the PLANCK scale and the age of the universe (t_u) is not mere numerology, but a physical principle.

Gravitationally lensed supernovae are rare transients that provide unique opportunities for time-delay cosmography and independent measurements of cosmological parameters. The unparalleled sensitivity of the James Webb Space Telescope (JWST) enables searches for multiply imaged supernovae in galaxy cluster fields, but the expected discovery rate depends strongly on the observing strategy adopted.

We forecast the detection rates of gravitationally lensed supernovae in JWST cluster observations. We simulate JWST observations with different strategies to quantify the detectability of lensed supernovae as a function of redshift, magnification, extinction, and observational parameters. Using these simulations, we optimize the filter selection for lensed supernova searches and combine the resulting detection efficiencies with supernova rate estimates.

Our predictions combine two complementary approaches: one based on known multiply imaged galaxies behind galaxy clusters and their associated supernova rates, and another based on the expected number of lensed supernovae exploding in a given volume behind cluster lenses. By combining these approaches, we aim to provide robust predictions of the number of multiply imaged supernovae that can be discovered with JWST and identify observing strategies that maximize their scientific return. We further explore the expected suitability of detected events for time-delay cosmography to account for the fact that not all lensed supernovae provide equally valuable cosmological constraints.

Einstein correctly predicted that mass (the 'lens') bends light around it. The largest lens is a galaxy cluster, which consists of up to hundreds of galaxies and a dominant dark matter component. A cluster lens magnifies a single galaxy image in the background into a larger and brighter version of itself called an "arc." For certain fortuitous lensing geometries, a single galaxy image can also be photocopied into multiple locations into an "image system."  Much of my career was spent studying these massive gravitational lenses.

Benefitting from the lensing effect, I have discovered some of the first image systems that extend back to when the universe was less than one billion years old, enabling detailed studies of objects in the distant universe. By taking advantage of the high lensing magnification factors, the impacts of star formation within the lensed galaxies were quantified, and at a spatial resolution that cannot be achieved in any other way. Maps of the distribution of the dark matter in the lens were also constructed for several galaxy cluster lenses for the first time.

In 2023, just one year after the launch of the James Webb Space Telescope (JWST), I discovered an exploding star or "supernova" that is situated behind a galaxy cluster lens and is also of known intrinsic brightness, called "SN H0pe". As a result of the lensing effect, light from this single supernova appeared in three different locations, each one depicting the supernova at a different snapshot in time during the explosion. The difference in the arrival time of the photons to each of these locations, combined with other information obtained by the observations, yielded a value for the current rate of expansion of the universe, called the "Hubble" constant.

Differences have arisen between the late-time and early-time values for the Hubble constant that raise doubts about its validity. This "Hubble tension" has become one of the most important questions in the field of Cosmology.  The late-time measurement of the Hubble constant from SN H0pe is impactful for offering an independent measurement that can elucidate this Hubble tension.  This experiment to measure the Hubble constant for SN H0pe was carried out successfully for only the second time in history, and for the first time using a Type Ia supernova. This work is leading to a better understanding of this fundamental parameter that describes our universe.

The advent of the JWST and its phenomenal near-infrared sensitivity and spatial resolution has enabled us over the last few years to uncover a new and rich population of extremely red point-sources at high redshifts dubbed "Little Red Dots" (LRDs). Many properties of LRDs, to their very origin, remain mysterious and they remain one of the most prolific fields of JWST research into the early Universe. Ever since their first discovery, strong gravitational lensing (SL) has represented a sheer treasure trove of information for LRD science through the magnification, which enables us to probe fainter and smaller objects, and time-delays between multiple images, which allow us to measure long-term variability in humane time scales. While many LRDs are known in blank fields, the sample of multiply-imaged LRDs remains limited to one -- A2744-QSO1. With the VENUS JWST cycle 4 program delivering new JWST imaging and spectroscopy of 60 SL fields, the time has come to expand this sample. In VENUS, we have thus-far detected a handful of new multiply-imaged LRDs at z~3-6, and more SL fields are being observed almost every week. In my talk, I will give an overview of what gravitational lensing can do for LRD studies, and present our ongoing efforts to build a statistical sample of lensed LRDs, as well as some preliminary results. With several magnified and multiply-imaged LRDs, we will be able to investigate in unprecedented detail where they fit into our picture of galaxy and black hole formation and the co-evolution of galaxies and black holes.

I will present highlights from our group's studies of the resolved stellar population of five Local Group disk galaxies: Milky Way (MW), Andromeda (M31), Triangulum (M33), Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC). These studies include the SPLASH and TREX spectroscopic surveys of several thousand stars in the disk and halo of M31 and M33, respectively, that span a wide range of stellar masses and therefore stellar lifetimes. The SPLASH and TREX surveys of M31 and M33 were carried out with the DEIMOS instrument while the spectroscopic follow up of RR Lyrae stars in the distant MW halo was carried out with the ESI instrument; these two instruments are on the Keck II 10-meter telescope on the summit of Maunakea on the Big Island of Hawaii. The following papers describe the key findings that I will present in my talk: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Turbulence is understood to be  present throughout the entire interstellar, and indeed inter-galactic, medium. Typically, turbulence acts to transport energy from large-scale motions to ever smaller-scale motions until the so-called dissipation scale is reached. In hydrodynamics this scale is usually defined by the scale at which viscosity becomes important. In magnetohydrodynamics (MHD), which is what is of relevance to the interstellar medium, this dissipation takes place both through magnetic energy dissipation and kinetic energy dissipation. The former happens through resistivity converting the energy in electric currents to heat, while the latter occurs through viscosity converting the kinetic energy in fluid flow to heat. This heating can be of critical importance to, for example, planet formation and star formation. It has been common practice to presume that magnetic energy dissipation occurs primarily where the electric currents are most intense - in so-called “current sheets”.

In this work we re-address the issue of dissipation of magnetic energy in turbulence, focusing specifically on turbulence in star forming regions, using a single fluid, non-ideal MHD approach. In the context of early uses of current density as a proxy for dissipation, we study the differences between the distribution of the current density and the dissipation rate. We confirm that the current density is a poor tracer of dissipation of electromagnetic energy. We quantify and explain the discrepancy between the two distributions, with high current density structures having a significantly harder size spectrum and little overlap with high dissipation structures. We also briefly investigate the role of the Hall effect in these dissipative processes.

We report a 325 (+24, -4) day quasi-periodic oscillation (QPO) in the X-ray emission of the blazar MRK 421 based on Swift-BAT data. This is a confirmation of the QPO reported by Smith et al. (2023), who used RXTE ASM data over a different epoch (1995-2011). The X-ray QPO has been seen for three decades in this object and its detection has also been claimed in other bands. The confirmation of the QPO was done using the EzTao Python toolkit, which builds on the Celerite software, allowing for more complicated modeling of the lightcurve. QPOs can be an important observable for accretion disks, which can be generated by a number of mechanisms, including disk corrugation and warps as well as other mechanisms, and can be modulated both by the orbital frequency and Lense-Thirring precession. In jetted sources such as MRK 421 they can also probe the coupling between the disk and the jet. We revisit various physical origins in both the disk and jet in the light of its extraordinary longevity.

We model spectral energy distributions of 261 X-ray sources to z ~ 5 in the North Ecliptic Pole Time Domain Field, extending prior XMM-Newton and NuSTAR analyses. Using the star-forming main sequence (SFMS) and black hole accretion rate (BHAR) frameworks, we find that SFRs generally lie below the SFMS while most BHARs exceed the population average, as expected for X-ray-selected samples. There is a strong correlation (+0.73) between SFR relative to the SFMS and specific AGN luminosity, $L_{mathrm{AGN}}/M_*$; galaxies with the highest $L_{mathrm{AGN}}/M_*$ exist at or above the SFMS. X-ray luminosity correlates with SFR (+0.80), revealing a star-forming and X-ray luminous ``cold quasar'' population consistent with dramatic, short-timescale accretion episodes. Low-mass galaxies show BHARs well above the population averaged value for their mass whereas high-mass galaxies' SMBHs accrete at the population averaged BHAR, suggesting ``growth spurt'' and ``maintenance-mode'' accretion, respectively. Traditional AGN classifications (obscured, unobscured, or radio-loud) do not reveal these distinctions, demonstrating the X-ray perspective's unique ability to identify rare AGN phases that are critical for the instantaneous link between galaxies and their SMBHs.

The presence of microscopic, solid, charged particulate matter immersed in a background plasma, commonly known as “dusty” or “complex” plasmas, has been the subject of extensive research over the last four decades due to its relevance to laboratory, industry, near earth space, inter-planetary dust in our solar system, and astrophysical systems. These include both space phenomena such as noctilucent clouds, dust-tails of comets, rings of the outer planets of the solar system and affects astrophysical phenomena such as radiative transfer, thermodynamics, surface chemistry and large scale flows and dynamics of astrophysical systems at various scales. 

The Magnetized Plasma Research Laboratory (MPRL) at Auburn University investigates fundamental plasma and complex/dusty plasma phenomena over a large range of parameter regimes from unmagnetized plasmas to strongly magnetized plasmas. MPRL's mission is to serve as an open access, multi-user collaborative research facility for the dusty-, basic-, and fusion edge relevant plasma communities. The centerpiece of the laboratory is the Magnetized Dusty Plasma Experiment (MDPX) [1], a highly flexible plasma device with excellent diagnostic access to study the unique regime of high magnetic fields (up to 4 T), at relatively low density (~ 10¹⁴ – 10¹⁶ m^-3) and low electron (Te < 5 eV) and ion temperatures (Ti < 0.05 eV). Other instruments in MPRL include ALEXIS and ALISSA, inductively and capacitively coupled plasma sources respectively to simulate space plasmas, conditions for reentrant vehicles and perform basic plasma experiments on waves and instabilities. In addition, we have a wide variety of “tabletop” scale unmagnetized, low temperature capacitively coupled plasma devices that can be adapted to the high magnetic field MDPX device. This allows us to host several external collaborators in our lab. 

This presentation will summarize some recent novel studies at MPRL such as pattern formation of magnetic field aligned filamentary structures at high magnetic fields [2], discuss the very rich and complex, turbulent-like dynamics associated with the formation of these magnetic field aligned filamentary structures [3] and finally show how microscopic, charged dust particles can be used as a diagnostic [4] to reveal the electrostatic nature of these filamentary structures. 

In addition, we would like to showcase the workforce development aspects of MPRL, where we not only train our own undergraduate and graduate students in research, but also actively work with and encourage research by undergraduate and graduate students of our external collaborators. Recently, we have formed the Strategic Plasma Innovation Network (SPI-NET), which is a consortium of institutions that can engage in fundamental plasma science research with a focus on processes that lead to self-organization and pattern formation in magnetized plasmas and dusty plasma and with a goal to grow the plasma science workforce. We aim to provide resources such as free academic consultation, time limited access to our devices in MPRL and minimal travel awards to try to lower the entry barrier for researchers across all levels of academics.

Large-scale structure in the early Universe remains poorly understood, as simulations struggle to reproduce the most extreme overdensities observed at high redshift. Protoclusters, the progenitors of present-day galaxy clusters, are key testbeds for studying how galaxies and their environments co-evolve during the early stages of structure formation. Massive submillimeter galaxies (SMGs) and quasi-stellar objects (QSOs) have long been proposed as signposts of protocluster environments due to their association with massive dark matter halos. We investigate whether six massive SMGs and five QSOs reliably trace overdense environments at z~4-5 and whether these structures can plausibly evolve into present-day galaxy clusters. Using deep JWST NIRCam/MIRI and Hubble imaging, we identify companion galaxies through photometric redshifts and find eight significant overdensities, with galaxy number counts 4-16 times larger than typical field fluctuations at these redshifts. Halo masses inferred through abundance matching are consistent with the expected progenitors of massive present-day galaxy clusters. The stellar mass function (SMF) of the TRICEPS environments shows an excess of massive galaxies, log₁₀(M_star/M_solar) > 10.2, relative to the field, while most member galaxies have star formation rates consistent with the field star-forming main sequence. Comparing the TRICEPS SMF with those of clusters at z~1 and z~0, we find that volume contraction alone cannot explain the observed evolution. We present a phenomenological model that shows that ongoing star formation combined with a mass- and redshift-dependent power-law quenching rate can evolve the TRICEPS SMF toward the shape of both galaxy cluster SMFs. Our results show that massive galaxies are effective signposts of overdense environments ~1.5 Gyr after the Big Bang. The overdensities traced by the TRICEPS galaxies are plausible progenitors of lower-redshift galaxy clusters, making them excellent laboratories for studying the early "growing" phase of cluster evolution.

I will describe the Roman eXtreme Deep Field (RXDF) program that has been allocated 386.41 hours in Cycle 1-2 of the Roman Space Telescope. The program will do extremely deep imaging in an area close to the North Ecliptic Pole (NEP) to depths comparable to the Hubble Ultra-Deep Field (HUDF) but over an area 60x larger in size, reaching 5-sigma limits of AB = 30 mag in RZYJH, 29 mag in F and 28 mag in K. Thanks to its large, contiguous area (1243 arcmin^2), the RXDF will be the least impacted by the cosmic variance and will be ideal for the clustering analysis of rare objects that need large volumes for statistics (e.g., galaxies/AGNs at z>10).  The RXDF will enable a slew of unprecedented studies on galaxies and accreting SMBHs from the cosmic “dawn” to “noon” to “afternoon”.  The RXDF is also designed to exploit Roman's full potential in time-domain science. The observations will be spitted into three major epochs separated by ~1 year, and each major epoch is further divided into three sub-epochs that are ~10-12 days apart. One major focus of the RXDF time-domain science is supernovae (SNe) at z>2.5. It is expected that the RXDF will result in ~120 SNe Ia (possibly to z ~ 5); ~400 CCSNe total (~10 at z > 6); ~80 SLSNe total (possibly to z~14 and containing Pop-III SNe). The RXDF will also enable a broader range of science topics, including the studies of Galactic brown dwarfs and moving objects in our Solar system.
 

The mass--metallicity relation (MZR) encodes the baryon cycle that regulates galaxy growth, but at the low-mass end (log M* < 9) it is poorly constrained and the fundamental
metallicity relation appears to break down. It is not yet clear whether this reflects a real departure from equilibrium or the selection and calibration limits of the samples used to find it. Settling this requires calibrated, joint posteriors on stellar mass, star-formation history, and stellar and gas-phase metallicity for a large, selection-unbiased sample --- which current SED codes cannot deliver at survey scale. I am developing  UberSED, an amortized neural posterior estimation pipeline for the DESI Bright Galaxy Survey, built on a Prospector forward model with the Cue nebular emulator that decouples gas-phase from stellar metallicity. Using a Spender autoencoder to compress each spectrum, I have already identified the DESI galaxies this forward model cannot reproduce. In my second year, I will repair the model where it fails, train the estimator, and verify that its posteriors are statistically calibrated.  With calibrated posteriors for ten million galaxies, I will measure the low-mass MZR and its scatter on a single self-consistent scale and test whether dwarf galaxies depart from equilibrium.

Type Ia supernovae—the thermonuclear explosions of white dwarfs—can be standardized as cosmic distance markers and have played a central role in revealing the accelerated expansion of the Universe. Until recently, however, spectroscopically confirming these events beyond redshift z = 2 was extraordinarily difficult.

We present JWST observations of SN 2022ret, discovered in NIRISS imaging behind the Abell 2744 galaxy cluster and followed with NIRCam imaging and NIRSpec spectroscopy. Emission lines from its host galaxy establish a redshift of z = 2.56, corresponding to light emitted roughly 11 billion years ago. This makes SN 2022ret one of only four spectroscopically confirmed Type Ia supernovae at z>2. Gravitational lensing by Abell 2744 magnified the event by a factor of approximately 1.7.

Although SN 2022ret was discovered after maximum light and its NIRSpec spectrum was obtained more than 60 rest-frame days after peak brightness, independent analyses of its light curves and spectrum consistently classify it as a normal Type Ia supernova. After correcting for lensing and other luminosity-related effects, its peak brightness is consistent with that of typical nearby Type Ia supernovae.

Combining SN 2022ret with two other z > 2 events that satisfy conventional cosmological color criteria, together with a Cepheid-based luminosity calibration, yields H₀ = 71.6 ± 3.3 km s^-1 Mpc^-1, intermediate between early- and late-Universe measurements. The present sample provides no statistically significant evidence for evolving or phantom dark energy. These results demonstrate JWST’s ability to transform supernovae from the Universe’s first few billion years into cosmological probes, while emphasizing the need for larger samples from future JWST, Roman, and Rubin surveys.

The combination of sensitivity and spatial resolution has made JWST a consequential strongly-lensed supernova finder despite limited epochs and coverage. In particular, observations of galaxy clusters have delivered multiple supernovae viable for cosmography, in which the measured ‘time-delay’ between multiple images enables inference of the Hubble Constant. In this talk, I will first give an overview of the current state of supernova time-delay cosmography, including existing measurements and challenges for making this measurements. I will then highlight the success of the recent JWST programs, such as the cycle 4 program VENUS, to yield new cosmography grade supernovae. Given this growing sample, I will provide forecasts and outlook on future cosmographic measurements. Finally, I will highlight how systemtatics relating to strong lensing models can be improved. In particular, I will showcase the power of strongly lensed Type Ia supernovae, such as SN H0pe, which enables measurement of the lensing magnification to break lensing degeneracies.

Time-domain astronomy is entering a new era. With JWST, we can now discover and study supernovae in the early universe, while the Rubin Observatory and the Nancy Grace Roman Space Telescope will find rare transients across wide areas and in unprecedented numbers. These complementary facilities are transforming the transient sky into a laboratory for precision astrophysics and cosmology. In this talk, I will show how these observations are opening new ways to study cosmic expansion and probe the physics of the early universe. High-redshift Type Ia supernovae allow us to test the stability of the standard candles used to trace cosmic acceleration, while strongly lensed supernovae provide an independent route to cosmological distances through time-delay cosmography. I will highlight recent JWST results on both classes of objects and show how they foreshadow the next decade of time-domain astronomy. Together, JWST, Rubin, and Roman will significantly enhance the role of the transient universe as a precision tool for cosmology.

Over 6,000 exoplanets—planets beyond our Solar System—have been identified. These worlds span a remarkable range of sizes, temperatures and atmospheric compositions, including detections of exotic clouds made from glass, molten iron or rubies [1-3]. Because exoplanets are so distant, we cannot usually image them directly. Instead, we infer their atmospheric properties by analysing the tiny fraction of starlight that passes through or is emitted by their atmospheres. Interpreting these spectra allows us to probe atmospheric composition, temperature, and weather, making accurate atmospheric models essential for understanding these distant worlds.

Clouds and hazes play a crucial role in shaping the detectable spectra of planetary atmospheres through absorption and scattering [4]. While many exoplanet models assume these aerosol particles to be spherical, we know from Earth-based measurements that aerosols are likely to form into much more complex fractal aggregate structures. In this talk, I present a recent upgrade that we have made to the widely used cloud code VIRGA (v2.0), enabling characterization of irregular, non-spherical particles while retaining computational efficiency. Our new release incorporates, for the first time, the optics and dynamics of fractal aggregates.

I also present initial results that reveal the measurable influence of particle shape on observed transmission and emission spectra, and I summarize the behaviour of fractal aggregate particles in warm Neptune, hot Jupiter, and brown dwarf atmospheres [5]. I conclude by discussing the important community implications for the interpretation of observational data and the modelling of planetary atmospheres.

The Global Supernova Project is a collaboration between more than 200 scientists worldwide, studying approximately 150 nearby supernovae per year using the Las Cumbres Observatory global network of robotic telescopes combined with more than 20 other facilities, including HST, JWST, SOAR, Gemini, Keck, Rubin, and more.  We work jointly with the Shadow survey using DECam to find SNe in nearby clusters jointly with LSST, and the Public AEON Spectroscopic Survey for Transient Astronomy (PASSTA) using SOAR to get spectra of nearby supernovae.  We have also worked with the Keck Infrared Transient Survey, and PESSTO using the ESO 3.6m.  I will discuss our recent result in Nature —the discovery of Lense-Thirring precession in a superluminous supernova, as well as recent advances in determining the progenitors of SNe Ia.  Finally, I will highlight how public software tools we are creating allow many surveys to work together, trigger observations, and share data more efficiently in the LSST era, including the TOM Toolkit and Hopskotch/HERMES. 

We present James Webb Space Telescope (JWST) and Atacama Large Millimeter Array (ALMA) observations of PJ0846+15, The Koi Pond, a strongly lensed protocluster core at Cosmic Noon. This field offers a magnified view of 11 dusty star-forming galaxies (DSFGs) all at z = 2.67 (within ∆V = 800 km s−1) spanning a projected extent of > 300 kpc lensed by a z = 0.77 foreground cluster. NIRCam and ALMA Band 6 continuum measurements map the stellar distribution and thermal dust emission respectively at a spatial resolution of ∼0.15′′. This multi-wavelength analysis reveals a diverse population of DSFGs with a wide range of morphological features including disks, bulges, spiral arms and bars, evidence for interactions like merger pairs and tidal tails/streams and identification of several clumps/stellar clusters. Comparing the rest-frame J- band continuum (F444W) vs (i-J) color (F277W−F444W), we find a wide range of values, suggesting a >1-dex spread in stellar mass and∆Av > 1 mag. The DSFGs members exhibit varying dust sizes relative to stellar emission - from compact dusty cores to galaxy wide dust emission. Resolved color maps of individual sources showing a spread as high as F277W−F444W= 2 suggesting complex stellar-to-dust geometry. Although gas-rich mergers are identified in the core, the most red and dust emitting members are disks exhibiting clumpy
structure indicating secular growth can drive these starburst events. Such a remarkable range in properties within this sample suggest DSFGs in protocluster core environments follow diverse evolutionary pathways towards their transition into quiescent, elliptical cluster galaxies.

Ultra-Diffuse Galaxies represent some of the faintest galaxies that we can observe, with average surface brightnesses well below the typical sky level. They are also some of the most numerous, with thousands identified in local galaxy clusters [1]. Some are thought to hold remnants of early intense star formation, with billion-year-old stellar populations [2] and large globular cluster populations [3]. However, the evolution of these systems is not well understood, especially the tidal interactions between them and the cluster environment in which they are typically found [4]. In addition to providing insight into galaxy formation physics at small scales, study of these systems can shed light on the nature of dark matter and the connection between dark matter halos and galaxies, given their high dark matter fractions [3]. I will discuss how observations of these systems at higher redshift, possible with observations using JWST, can teach us about their formation and evolution. In particular, recent work has shown that Ultra-Diffuse Galaxies in higher redshift clusters are more similar to field dwarf galaxies (with younger stellar populations and a wider range of sizes) than older systems observed at low-z [5].